Chemical sensors are widely used in environmental and automotive applications for the monitoring and detection of hazardous or pollutant emissions, such as freon, ammonia and automobile exhaust gases. For example, chemical sensors are employed in the automotive service industry to monitor the performance of an automobile's exhaust gas recirculation (EGR) valve, a process commonly known as a "smog check." The EGR valve controls the emission of carbon monoxide, carbon dioxide, hydrocarbons released from unburned fuel, oxygen, as an indicator of a fuel system's air consumption, nitric oxide and other gases.
A typical system for testing exhaust emissions employs sensors that screw into the gas intake or manifold block. There are several disadvantages of a threaded sensor-manifold mating protocol. First, a threaded-screw connection limits the type of electronic interface that can be made with such a sensor. There are multiple electrical connections that are required between the sensor and the sensor circuitry (on a PC board) and between the circuitry and system inputs (e.g., power, ground, etc.) and outputs (e.g., digital display, etc.). Because of the need for multiple connections, a card-edge connector would be ideal. However, because a threaded mating scheme has inconsistent and unpredictable fitting tolerances, depending on the amount of torque applied, a card-edge connector is not practical. Instead, these multiple electrical connections are possible only with a "crimp and poke" connector, such as manufactured by Molex. These type of connectors are relatively bulky and are consequently subject to repeated bending and flexing. Repetitious flexing of wire can result in unreliable electrical contacts and therefore unreliable sensor performance.
Another disadvantage of prior art gas sensor-manifold connections, is the unreliability of the seal between the two. Of course, the more air-tight the seal, the more accurate the sensor measurement. Screw-in sensors are not fully air-tight if not correctly seated. Even with the use of a washer or o-ring seal, the results are dependent upon the tightness of the screw connection and the size of the washer employed.
Accordingly, it is a general object of the present invention to provide an improved sensor support subassembly.
Another object of the present invention is to provide a sensor support subassembly having a more flexible and reliable means of coupling the sensor to the gas manifold.
Another object of the present invention is to provide a sensor support subassembly having a highly reliable electrical connection scheme that improves upon the prior art.
Another object of the present invention is to provide a sensor support subassembly with an improved air-tight seal between the sensor and manifold block.